Operation of conventional computer equipment, for example, is typically accompanied by the generation of radio frequency and/or electromagnetic radiation in the electronic circuitry of the computer system. If not properly shielded, such radiation can cause considerable interference with entirely unrelated equipment. Accordingly, governmental regulations, as well as sound manufacturing practice dictate that the sources of radio frequency and/or electromagnetic radiation within the computer system be effectively shielded and grounded.
In instances where the radiation-generating circuitry is permanently or semipermanently housed in a container, effective shielding may be accomplished easily through proper construction of the enclosure structure. In certain cases, however, effective RF interference (RFI) or electromagnetic interference (EMI) shielding present somewhat more difficult problems. This is particularly true, for example, where the equipment housing is provided with a readily openable access panel or door, for servicing or other routine access. In addition, large numbers of computer installations have been made in the past without a full understanding of the effect of partially unshielded enclosures, particularly involving access doors. Accordingly, many manufacturers and/or users of older computer equipment are attempting to upgrade the level of RFI/EMI shielding through retrofit installation of shielding devices around the access openings. To this end, it has been known heretofore to provide a clip-on shielding device adapted to be pressed or clipped onto an exposed sheet metal edge, typically provided at the peripheral edges of an access door of a conventional sheet metal housing or enclosure for a computer installation. A device of known construction includes a continuous, roll-formed strip metal clip, to one side surface of which has been bonded a resilient tubular element of electrically conductive elastomer. The clip is constructed so as to be applyable over the edge of sheet metal door or panel and retained in place by frictional gripping action of the roll-formed clip. The configuration of the element is such that the resilient tubular elastomer, bonded to the clip, is brought into contact with a fixed surface of the enclosure, when the door or panel is closed, effectively sealing off the narrow gap otherwise typically provided between a door or panel and the oppositely facing surface areas of the housing.
Known clip-on shielding devices as described above, while reasonably effective for many applications, have been characterized by certain shortcomings. In this respect, the known devices have proven to be somewhat inconvenient to install. Moreover, and perhaps of greater importance, the presence of a good quality coating over the metal surface tends to inhibit good electrical contact and, in cases, may reduce or negate the effectiveness of the shielding strip, unless special provisions are made to remove areas of the coating down to bare metal.
In accordance with the present invention, specific improvements are incorporated in a clip-on strip of otherwise known design to the end of making the clip-on device significantly easier to install and assuring in all cases the presence of an excellent conductive contact between the rolled metal clipping element and the door or panel to which it is secured. The improvements of the present invention are achieved with little or no increase in the cost of manufacture of the device, yet result in savings in time and cost in installation while assuring improved operating performance from the device.
For a better understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred emdodiment and to the accompanying drawings.